In a development that may lead to better treatments for modern-day childhood cancers, researchers have found a way to reveal the genetics of tumor samples dating back to the 1920s. The team published their findings in The Lancet.

The good thing about rare childhood cancers is that they’re rare, which means that few children will get them. But the bad thing is that that same rarity produces very few samples, which makes them harder to study, which in turn makes them near-impossible to treat with any scientific confidence.

“The treatment regimens for children with rare cancers are essentially made up,” lead author Sam Behjati of the Wellcome Trust Sanger Institute told Nature. “If you’ve got three or four patients nationally, how are you ever going to conduct a reasonable clinical trial?”

The ideal situation—more tumor samples but fewer sick kids—may be less paradoxical than it sounds, as Behjati and his colleagues have figured out a way to grab genetic information from old tissue samples. And when we say old, we mean really old.

The Great Ormond Street Hospital for Children in London—which was saved from closure shortly after it opened thanks to a fundraiser by Charles Dickens—has been collecting samples from young patients since the mid-19th century, long before we had the technology to preserve them in any useful way. Then, in the early 20th century, scientists started dousing their samples in a chemical called formalin and embedding them in paraffin wax. The technique worked so well that researchers still use formalin-fixed paraffin-embedding (FFPE) today.

DNA is delicate stuff, and it tends to fall apart over time. Previous researchers have had some luck extracting DNA from FFPE tissue samples, but the oldest of these was only 32 years old.

The authors of the recent paper wondered if they could sample older specimens. They pulled three potential tumor samples from the hospital’s archives dating to the 1920s. One had been tentatively diagnosed as a lymphoma; one as a skeletal muscle cancer called rhabdomyosarcoma; and another as a blood-vessel tumor called cellular capillary hemangioma.

They scraped a tiny bit of tissue from each and ran them through a comprehensive genetic sequencing program.

The old-school preservation technique had done its job “remarkably,” the authors write, and each old sample’s genetic code matched the profile of its modern-day counterpart. This development “paves the way” for studying rare tumors, they say, and could shed light on the long-ago mutations that led to the cancers we face today.

[h/t Nature]